Photomicrographs of aneurysmal necks at 3 months. A, From the PA group, a thin neointima completely transverses the neck. The tissue appears to be concave to the aneurysm cavity (H&E, original magnification 40×). B, From the FBC group, there is a thin collagenous tissue that completely covers the neck (H&E, original magnification 60×). C, From the Ad-BMP-13 group, there is moderately thick collagenous tissue completely across the neck. (H&E, original magnification 60×). All of the tissue traversing the necks is lined with a monolayer of cells contiguous with the endothelium of the parent arteries.